Currently, most digital cameras use a zoom lens and a single color image sensor to capture still and motion images. The captured images are then digitally processed to produce digital image files, which are stored in a digital memory in the camera. The digital image files can then be transferred to a computer, displayed, and shared via the Internet. The digital camera can be included as part of a mobile telephone, to form a so-called “camera phone”. The camera phone can transmit the digital image files to another camera phone, or to service providers, via a mobile telephone network.
Small camera size and a large “optical zoom range” are two very important features of digital cameras. Users prefer to have a large zoom range (e.g. 5:1 or greater) rather than a limited zoom range (e.g. 3:1 or smaller). Unfortunately, providing a large zoom range lens, without sacrificing the quality of the captured images, increases the size of the digital camera. Large zoom range lenses are also more costly. Thus, there are fundamental trade-offs between small camera size, large zoom range, and low camera cost which must be made when designing a digital camera. With higher cost cameras, such as single lens reflex cameras, these problems are sometimes addressed by using multiple interchangeable zoom lenses, such as two 3:1 zoom lenses, e.g., a 28–70 mm zoom and a 70–210 zoom. Such an option, which has its own problems in user inconvenience, is nonetheless not available for low cost digital cameras.
The prior art of most interest can be separated into two categories: image capture systems that use multiple lenses, usually two, having the same focal length and image capture systems that utilize multiple lenses, also usually two, having different focal lengths.
Addressing the first category, some digital cameras use multiple image sensors to form a color image. In most cameras of this type, a single lens is used to provide an image of the scene, which is then separated into multiple colors by a prism beam splitter. Multiple monochrome image sensors are used to capture red, green, and blue color separation images. However, as disclosed in U.S. Pat. No. 6,611,289, entitled “Digital Cameras Using Multiple Sensors with Multiple Lenses” and issued Aug. 26, 2003 in the name of Yu et al., it is possible to use multiple image sensors and multiple lenses to provide color separation. However, this patent disclosure teaches that the lenses all have the same focal length, and are all used together, in order to simultaneously capture the different color components of the image Some digital imaging systems also use multiple image sensors and multiple lenses to capture different portions of the digital image. Such a system is disclosed in U.S. Published Patent Application No. US20020163582 A1, entitled “Self-calibrating, Digital, Large Format Camera with Single or Multiple Detector Arrays and Single or Multiple Optical Systems” and published Nov. 7, 2002 in the names of Gruber et al. In one embodiment disclosed in this published patent application, a large format digital camera exposes multiple detector arrays using multiple lens systems to acquire sub-images of overlapping sub-areas of large area objects. The sub-images are stitched together to form a large format digital macro-image. However, all of the lenses have the same focal length, and all are used simultaneously to capture the different sub-areas of the image.
Stereo film cameras and stereo electronic cameras are known in the prior art. These cameras typically have two horizontally separated lenses of the same focal length, which focus two slightly different images of the scene onto two image sensors or two frames of film. Such a system is disclosed in commonly assigned U.S. Pat. No. 4,989,078, entitled “Still Video Camera for Recording Stereo Images on a Video Disk” and issued on Jan. 21, 1991 in the name of K. Bradley Paxton. The two images provide a so-called “stereo pair”, which simulates the slightly different perspectives that a person's left and right eyes would see when viewing the scene. In the aforementioned patent disclosure, the two lenses are designed to provide the same magnification, and both are used to simultaneously capture the left and right eye images on a pair of image sensors in order to achieve a stereo effect.
Film cameras that use multiple lenses to capture multiple images at the same time are also known in the prior art. For example, some instant film cameras used to produce identification pictures can capture four small images simultaneously on the same piece of instant film. The four lenses in these cameras provide the same magnification, and all are used to simultaneously capture the four images.
According to the second category of prior art, film cameras that include two or more lenses to provide two or more different focal lengths are also known in the prior art. For example, such cameras can use two different fixed focal length lenses which are slid in front of the same film plane. This provides an inexpensive “two-position zoom” capability, that is, two fixed focal length lenses that provide, e.g., the wide angle and telephoto angle settings of a corresponding zoom lens. In another example, in U.S. Pat. No. 4,097,882, entitled “Multiple Lens Camera Having Lens-position Controlled Focal-length Adjustment” and issued Jun. 27, 1978 in the name of Engelsmann, a “110” size pocket film camera has a carrier mounting three or more lenses of different focal lengths that can be selectively moved transverse to the optical axis of the camera so as to place any one of the lenses in an operating position relative to a film plane.
Digital cameras that include two lenses to provide two different focal lengths are also known in the prior art. A lens turret is popularly used to obtain multiple focal lengths in a camera. However, in the case of a digital still camera or especially in the case of mobile phone digital camera, lens modules are required to be extremely small due to the limited space for the lens module. U.S. Pat. No. 6,804,460, entitled “Lens Turret with Back Focal Length Adjustment” and issued Oct. 12, 2004 in the names of Oshima et al., describes a lens turret that is said to be extremely compact and flat in size and suitable for digital still cameras and mobile phone digital cameras. The lens turret is rotatable around an axis and has a wide-angle lens and a telephoto-angle lens mounted thereon, and a driving mechanism rotates the lens turret so that one of the lenses can be set at a picture taking position opposite an image sensor. By means of back focal length adjustment, the position of the lens with the shorter focal length can be fixed on the lens turret at the same level thereon as the lens with the longer focal length.
It is also known to use a two lens arrangement in a film scanner, where two lenses with different combinations of focal lengths are used to capture variable sized images. For instance, in commonly assigned U.S. Pat. No. 5,929,903, entitled “Multiposition Lens Mechanism for a Scanner” and issued Jul. 27, 1999 in the name of R. H. Kiesow, a removable digital camera, which is tethered to a computer, is supported in a housing in a film scanner in the optical path of a multiposition lens assembly having a single focal length lens and a zoom lens. The lens assembly positions the lenses in the optical path of the camera for scanning different sized images, e.g., two or more film format sizes. However, these cameras, both film and digital, that use multiple focal length lenses share the characteristic of using only a single “sensor”, that is, a single film or a single electronic image sensor.
In U.S. Pat. No. 6,288,742, entitled “Video Camera Including Multiple Image Sensors” and issued Sep. 11, 2001 in the names of Ansari et al., a digital motion camera useful in teleconferencing includes two lenses and two image sensors. As disclosed in this patent, the first lens is an 8 mm fixed focus lens for providing a relatively wide-angle view of a room and the second lens is a 16 mm lens with manual focus control for providing high resolution document transmission capability. The first lens is oriented for a room view of a conference participant to provide face-to-face communication during a videotelephone conference, and the second lens is oriented at a substantial angle to the first lens for viewing a document, e.g., on a table. During a videotelephone conference, such a camera permits fast switching between an image of the room as seen through the first lens or an image of a document as seen through the second lens, without the need for expensive and tediously slow moving pan/tilt stages and/or a plurality of complete camera units. Another camera, the Sanyo S750 UMTS cellphone camera, has a similar kind of dual imaging capability, where an inwardly facing VGA imager captures an image of the caller using the cellphone while an outwardly facing 1 megapixel imager captures an image of a scene that the caller is looking at. Such cameras, however, are not useful in the environment of the present invention because the lenses are not collecting images from the same scene.
In U.S. Pat. No. 4,199,785, entitled “Electronic Zoom Feature” and issued Apr. 22, 1980 in the name of McCullough et al., a television system employs two (or more) fixed focal length vidicon cameras, one camera with a wide angle field of view and the other camera with a narrow angle field of view, and an electronic zoom feature for zooming between the two fields of view. The cameras are boresighted such that the field of view of the smaller field camera is within, and usually centered in the field of view of the larger field camera. The “zoom” is accomplished by manipulating the scan generators of the two cameras and expanding the central portion of the display with the image from the smaller field camera as the zoom amount is progressively increased. This system, of course, is an alternative to a single optical zoom lens, whose usage the patent disclosure discourages as they (optical zooms) are lower quality, more expensive and mechanically more complex than fixed focal length lenses. However, the inherent drawback of an electronic zoom is also low quality since the resolution of the electronic zoom feature ordinarily is limited by the number of scan lines available for zooming. Consequently, this patent disclosure is devoted to controlling the scan lines of the two vidicon cameras so as to be able to zoom without an effective loss of resolution.
In U.S. Pat. No. 5,051,830, entitled “Dual Lens System for Electronic Camera” and issued Sep. 24, 1991 in the name of Hoessle, a double focal length electronic camera (used on board a guided missile) includes a single lens system component having a short focal length section integrated into the center of a surrounding lens section having a long focal length, where each focal length section has its own dedicated picture array sensor. Here too, this lens system is a substitute for a single motor driven zoom, which the disclosure denigrates because of size, expense, heaviness, inherent complexity; furthermore, an optical zoom is “which is important—much too slow with respect to its use” (col. 2, line 1 of the Hoessle patent).
None of these prior art systems, and especially the multifocal length prior art systems, provide a sufficiently compact, low cost, large zoom range optical system for a small, lightweight and relatively inexpensive consumer digital camera. As especially pointed out in the aforementioned Hoessle patent, it is additionally desirable to avoid the slowness so typical of zoom usage and to be able to traverse a large zoom range quickly. What is therefore needed is a digital camera that provides a rapidly-operating extended zoom range without unduly increasing the size or cost of the digital camera.